The present invention relates to novel polymer polyols which have low viscosities and high hydroxyl numbers, and to a process for the preparation of these novel polymer polyols. These polymer polyols have hydroxyl numbers of ‰¥20, solids contents of about 30 to about 65% by weight and a viscosity that is less than or equal to: be [2.7c] . These comprise the reaction product of a base polyol, a preformed stabilizer and at least one ethylenically unsaturated monomer, in the presence of a free-radical polymerization initiator and at least one polymer control agent. The base polyol has a hydroxyl number of 60 to 1900, a functionality of 1 to 10, and an equivalent weight of 30 to 900.
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